Traveling wave tubes



May I, 1962 E. C. DENCH TRAVELING WAVE TUBES Filed Feb. 19, 195'.

l l l lu l (if /30 I62 /6/ United States Patent Ofiice 3,032,676 Patented May 1, 1962 3,032,676 TRAVELING WAVE TUBES Edward C. Dench, Needham, Mass., assignor to Raytheon Company, a corporation of Delaware Filed Feb. 19, 1957, Ser. No. 641,110 16 Claims. (Cl. 315--3.5)

This invention relates to a traveling wave tube and more particularly to a traveling wave tube in which the slow wave propagating structure or delay line, which forms one electric field-bounding electrode, is maintained at a potential negative with respect to another electric field-bounding electrode of the tube.

Prior traveling wave tubes have been constructed with a slow Wave-propagating structure and an auxiliary electrode spaced therefrom and coextensive therewith. An electric field is produced between this wave-propagating structure and the auxiliary electrode by maintaining the Wave-propagating structure at a potential which is positive relative to that of the auxiliary electrode. In such a tube, an electron beam is injected from a localized cathode near one end of the propagating structure into the interaction space between the propagating structure and the auxiliary electrode along a path which initially is nearer to the auxiliary electrode than to the propagating structure. As the electrons lose energy to the RF wave during interaction between the electron beam and the RF wave traveling along the wave-propagating structure, they move toward the positive wave-propagating structure and a considerable number of electrons actually may strike this anode structure. This arrangement has disadvantages, viz, for high efiiciency, the diflierence of potential through which the electrons pass under the action of the RF field should be relatively high; this means that the beam should be inserted along an equi-potential line disposed near the auxiliary electrode. Since the beam is injected at a point removed from the wave-propagating structure or anode where the longitudinal traveling RF field components are comparatively weak, the interaction is small, particularly in the case of amplifiers Where the input signal to the amplifier also may be quite small. Moreover, because of the collection of electrons on the anode, considerable energy must be dissipated from the slow wave-propagating structure. Dissipation of heat sometimes is difficult to achieve from complex delay structures, especially at high-power levels.

In accordance with this invention, the wave-propagating structure is maintained at a potential negative with respect to the auxiliary electrode, so that the latter becomes the anode toward which move the electrons which transfer energy to the RF wave. The auxiliary electrode, being a less complex mechanical structure than the wavepropagating structure, is easier to cool, thereby facilitating construction of the tubes, particularly when used at high-power levels. Furthermore, with the reversed potentials, the electron beam is injected into the interaction space much closer to the wave-propagating structure than with the conventional traveling wave tubes, and better coupling of the beam to the RF wave at the beginning of the tube occurs, with higher gain per unit length in the .case of amplifiers and greater power output in the case of oscillators.

Referring now to the drawings:

FIG. 1 is a central cross-sectional view, partly in elevation, of a first embodiment of a traveling wave tube according to the invention; FIG. 2 is a section view taken along line 2 -2 of FIG. 1;

FIG. 3 is a detail view of a portion of the electron gun mounting assembly and a portion of the delay line to which it is attached;

FIG. 4 is a cross-nectional view of a traveling Wave amplifier similar to the tube of FIG. 1, except for the additional input coupling means; and

FIG. 5 is a central cross-sectional view of a second embodiment of a traveling wave tube according to the invention.

Referring now to FIGS. 1 to 3, a traveling wave tube oscillator 10 is shown which comprises a periodic slow wave energy propagating structure or delay line 20, an elongated auxiliary electrode 30, sometimes referred to as a sole, maintained positive with respect to delay line 20, a lead-in assembly 40, an output coupling means 50', an electron gun assembly 60, further including at least a cathode 61 and a heater 62, and a transverse magnetic field producing means, a portion 81 of which is indicated in FIG. 1.

Delay line 20 is of the interdigital type including a plurality of interdigital fingers or members 24 and 24 which extend from oppositely disposed annular members 25 and 25', respectively; members 25 and 25 are secured by screws 26 to the shoulder portion of a cylindrical block 27 of a material such as copper. The members 25 and 25 include flange portions 28 serving to confine the electrode beam Within the interaction space 35 between the sole 30 and the delay line 20.

The sole 3% consists essentially of a cylindrical, thermally and electrically conductive ring 32 which is sealed hermetically to a pair of oppositely disposed cover plates 33 and 34 to form an evacuated envelope. A centrally located aperture 36 in the sole permits connection of the lead-in assembly 40 and allows for passage of external circuit-connecting leads in a manner to be shown subsequently.

Lead-in assembly 40 is arranged generally perpendicular to the cover plate 33 of tube 10 and includes an electrically conductive sleeve 4-2 which is sealed hermetically to cover plate 33. A section of vitreous tubing 43 connects sleeve 42 and a second metal sleeve 44, the free end of which is provided with a glass seal 45 for sealing tube 10.after evacuation. Sleeves 42 and 44 preferably are constructed of a material having an expansion coefiicient closely approximating that of tubing 43. Assembly 40 further includes an electrically conductive tube 46 which is inserted in an aperture in cover plate 33 and is secured to block 27. One end of tube 46 contains outwardly flared portion 47 which is connected to the inner surface of sleeve 44. The necessary leads for the electron gun are fed through supporting tube 46 and are insulatedly supported therefrom by one or more glass beads 49.

The interdigital delay line 20 is arranged concentrically with sole 3i) and is separated from circumferential wall 32 of the sole to form an interaction space 35 through which passes the electron beam generated by the electron gun. The coaxial output coupling means 50 is sealed in an opening of cover plate 34 and is isolated electrically from sole assembly 30 by an insulated bushing 51. The coaxial line 59 is brought out through an aperture in pole piece 81 of the magnetic field-producing means. The inner conductor 52 of the coaxial line 50 is connected to a finger at 0 near the end of the periodic delay line 20 adjacent the electron gun. Traveling wave tube 10 may be provided with a collector electrode 37, indicated in FIG. 2, for intercepting electrons after one traversal of the interaction space. This collector electrode may take the form of a projection from the inner periphery of sole 30. In some instances, however, the collector electrode may be omitted and the electron streammade reeutrant. Furthermore, sole 30 may be either primarily or secondarily emissive.

The electron gun assembly 60 for the tube of FIGS. 1 and 2 includes cathode 61, heater 62 and accelerating electrode 65, as shown in detail in FIG. 3. The cathode 61 shown, by way of example, as a rectangular body provided with a bore 63 in which heater 62 is inserted is positioned adjacent the delay line Cathode body 61 has at least the surface facing interaction space 35 coated with an electron-emissive coating and is positioned, for example, within a recess or slot 29' in one of the flanges 28 of delay line 20. Electrical connection to the cathode is made by means of a rigid electrically conductive stake 66 which may be made of molybdenum and spot-welded to one end of the cathode body. A cathode lead 48 is connected to stake 66. One end of heater 62 is connected to the inner wall of the cathode body while the other end of the heater is attached to a stake 67; the latter is mounted insulatedly by means of a bushing 64 on the top face of flange 28, as shown clearly in FIG. 3. A heater lead 19 is fastened to stake 67. The cathode 61 may be supported from flange 28 of delay line 20 by means of the flange 68 which may be secured, as by brazing, to the cathode body at One end, as shown in FIG. 3, and at tached, as by insulating screws (not shown), to a portion of the delay line flange 23. The cathode 61 is insulated from delay line 20 by means of an electrically insulating spacer 15. The accelerating electrode 65 which, in etfect, is an accelerating anode aiding in the production of the desired beam trajectory, is supported from flange 28 of delay line 20 by means of insulating screws 71; an electrically insulating spacer 17 provides the necessary electrical isolation between auxiliary electrode 65 of the electron gun and the delay line 20. Electrical connection is made to the accelerating electrode 65 by means of a stake 69 afiixed to one end of the accelerating electrode and electrically insulated from delay line 20 by virtue of its passage through an aperture 18 in one of the flanges 28. A lead 41 is attached to stake 69.

A suitable electrical field between delay line 20 and sole may be obtained by means of a voltage applied therebetween. The sole may be biased negatively with respect to the cathode by means of a source 95 of voltage connected between cathode lead 48 and sleeve 42. The cathode may, in some instances, be of the same potential as the sole. The delay line 20 is maintained at a potential negative with respect to both sole and cathode by means of a source 97 of voltage connected between metal sleeve 44, connected in turn to delay line 26, and cathode lead 48. The accelerating electrode 65 may be maintained at a potential positive relative to the cathode by means of a source 98 of voltage connected between leads 41 and 48.

A uniform magnetic field transverse to both the direction of the electric field between delay line 20 and sole 30 and to the direction of propagation of the electron beam is provided either by a permanent magnet or an electromagnet having cylindrical pole pieces 86 and 81 radially positioned on or adjacent the tube. Pole piece 80 is apertured to receive the lead-in assembly 40, while pole piece 81 is apertured to maintain symmetry of the magnetic field. The flux lines should be concentrated in the interaction space between sole 30 and delay line 20. By proper adjustment of the magnitude and polarity of the magnetic and electric fields, the electron beam may be made to follow an arcuate path about interaction space 35 under the combined influence of these transverselydisposed fields.

The radio frequency energy generated in the interaction space 35 traveling along delay line 2-0 sets up a highfrequency electromagnetic field which may be analyzed as a series of space harmonics, some of which travel in one direction, such as clockwise, along the delay line, and others of which travel in the opposite direction, such as counterclockwise, and all of which travel with different phase velocity. If the electron beam is caused to travel at the velocity substantially equal to that of the proper space harmonic, interaction of the beam and this space harmonic will result in the production of oscillatory energy within the tube. The energy travels toward the electron gun and is extracted at the gun end of delay line 20 by way of coaxial output line 56.

The tube 1 may be cooled by means of fluid cooling system which may, for example, include coils through which pass a fluid coolant circulated by any well known fluid pump. Coils 55 may be wrapped about the outer periphery of the angular portion 32 of the sole 30.

Although the traveling wave tube so far described is an oscillator, the invention equally is applicable to a traveling wave amplifier which, as indicated in FIG. 4, differs structurally from the oscillator shown in FIGS. 1 to 3 in further including an input coupling assembly 70, comprising inner and outer conductors 72 and 73, respectively. The inner conductor 72 is connected to one of the fingers of the delay line 20 at or adjacent the end or the delay line 20 electrically adjacent the electron gun, while the outer conductor may be insulated electrically from the sole member 32 by a bushing 75. The device shown in FIG. 4 serves as a forward wave amplifier. The position of the coupling assemblies 50 and may be interchanged if a backward wave amplifier is contemplated.

The input coupling means 70, as well as output coupling means 50, need not be restricted to a coaxial coupling; for example, the energy rnay be coupled to or from delay line 20 by means of a wave guide.

Another embodiment of the invention which, like that previously shown in FIGS. 1 to 3, may be used either as an amplifier or as an oscillator, is shown in FIG. 5. In the embodiment of FIG. 5, the traveling wave tube comprises a periodic slow wave energy propagating structure including several interdigital fingers or members 124 and 124, which extend from oppositely-disposed annular members 125 and 125, respectively; members 125 and 12.5 are secured by screws 126 to the shoulder portion of a cylindrical, thermally and electrically conductive ring 127 which, together with a pair of oppositelylocated cover plates 129 and 129 hermetically sealed thereto, define a vacuurntight envelope. The members 125 and 125 each include a flange portion .128 which serves as a beam-forming means, as already described.

The sole 130 may consist of a cylindrical member 131 of electrically conductive material which, for example, may be a solid block containing therein a fluid passageway 133. A central aperture is provided in sole member 131 to permit connection of fluid-cooling conduits and to pro vide for connection of external circuit-connecting leads. An electrically conductive sleeve 142 is sealed hermetically to a recessed portion of cover plate 128, and a glass tube 143 is connected at one end to sleeve .142 and at the other end to a second metal .sleeve 144 and is sealed off by a vitreous seal 145. A tubular member 146 extending through aperture 147 in plate 128 provides mechanical support for sole 130; one end of member .146 is aflixed to the periphery of an aperture 148 in sole member 131, and the other end of member 146 includes an outwardly-flared portion 146', which is connected to the inner surface of sleeve 144. An inlet conduit 151 and an outlet conduit 152 are brought through supported member 146 and seal and are supported within member 146 by a bushing 153. The conduits 151 and 152 connect at one end to passageway 133 in the sole member 131. It should be understood that the sole may be a hollow fluid-tight container provided only that the circumferential wall portion facing interaction space 155 through which passes the electron beam generated by the electron gun is made smooth "and concentric with delay line 121 A coaxial output coupling means 161 includes 'an outer conductor 161 sealed in an opening of back wall 127 of delay line 120 and includes also an inner conductor 162 connected to a finger of the delay line 120 at or adjacent the end of the delay line nearer the electron gun. The electron gun assembly 176 for tube 120 is. similar togun assembly 60 of FIG. 3 and is not shown in detail in FIG. 5.

Gun assembly 170 includes a cathode 172, a heater (not visible in FIG. 5) similar to heater 62 of FIG. 3, and an accelerating electrode (not shown for the sake of clarity) similar to electrode 65 of FIG. 3. The cathode, heater and accelerating electrode leads are indicated in FIG. 5 by reference numerals 177, 178 and 179, all respectively. Leads 177 to 179 are brought out through an electrically insulating bushing 180 mounted in wall 127. The electric field between the delay line 120 and sole 130 is provided by means of a voltage derived from voltage source 182. Source 182 may be connected between sleeve 142 and the cathode lead 177 where the cathode is the common reference point for circuit potentials. The sole may be maintained slightly negative with respect to the cathode by voltage source 184, connected between sleeve 144 and cathode lead 177. The cathode, however, may be at the same potential as the sole, in which case the voltage source 184 may be eliminated and the positive terminal of source 182 connected directly to sleeve 144.

The accelerating electrode may be maintained at a potential positive with respect to the cathode 172 by means of a voltage source 186 connected between cathode lead 177 and accelerating electrode lead 179. The magnetic field transverse to the electric field above referred to is provided by a magnet including magnet pole pieces 190 and 191.

As mentioned previously, the traveling wave tube 110 may be used as an amplifier provided a suitable input coupling means, similar to that shown in FIG. 4, is provided at or near the end of delay line 120 remote from the end to which coupling means 160 of FIG. 5 is connected. When a traveling wave amplifier is contemplated, the coupling means 160 may be used either as the input or output coupling means, depending upon whether beam interaction with a backward or forward wave is desired.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. For example, the invention is not restricted to a traveling wave tube of an arcuate configuration but may encompass a linear traveling wave tube such as described in Dench patent application Serial No. 382,133, filed September 24, 1953. It is accordingly desired that the appended claims be given -a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic and electric fields in said space for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along saidstructure, the average motion of said electron being along the length of said structure, said structure being maintained at a potential negative with respect to said electrode.

2. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from .and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space, said magnetic field being disposed substantially perpendicular to the direction of wave energy transmission along said structure, said structure being maintained at a potential negative with respect to said electrode.

3. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic and electric fields in said space for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said beam being injected into said interaction space along a region nearer said structure than said electrode, said electron source being positioned adjacent said structure, said structure being maintained at a potential negative with respect to said electrode.

4. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic and electric fields in said space for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with Wave energy traveling along said structure, said structure being maintained at a potential negative with respect to said electrode, said beam being injected into said interaction space along a region nearer said structure than said electrode.

5. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode .at least partially defining a continuous interaction space therebetween, said electrode being capable of electron emission, means including a magnet and a potential source coupled to said structure and said electrode pro ducing mutually transverse magnetic and electric fields in said space for directing a beam of electrons along said interaction space in energy exchanging relationship with wave energy traveling along said structure, and said structure being maintained at a potential negative with respect to said electrode.

6. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic .and electric fields in said space for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with Wave energy traveling along said structure, said beam being injected into said interaction space along a region nearer said structure than said electrode, said structure being at least partially surrounded by said electrode, said structure being maintained at a potential negative with respect to said electrode.

7. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship With Wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and ma netic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said structure being at least partially surrounded by said electrode said magnetic field being disposed substantially transverse to the direction of wave energy transmission along said structure, said structure bein maintained at a potential negative with respect to said electrode.

8. A beam reentrant traveling Wave electron discharge device comprising a periodic slow Wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially cextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic and electric fields in said space for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, the average motion of said electrons being along the length of said structure, said structure being maintained at a potential negative with respect to said electrode, said structure including a portion extending from opposed portions of the periphery thereof for confining said electron beam Within said interaction space.

9. A beam reentrant traveling Wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetWeen, an electron source, and means including a magnet and a potential source coupled to tionship with wave energy traveling along said structure, 7

said structure being at least partially surrounded by said electrode, the average motion of said electrons being along the length of said structure, said structure being maintained at a potential negative with respect to said electrode, said structure further including a. portion extending from opposed portions of the periphery thereof for confining said electron beam Within said interaction space.

10. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propagating "structure for ransmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, and means including a magnet and a potential source coupled to said structure and said electrode producing mutually transverse magnetic and electric fields in said space for directing .a beam of electrons emanating from said source along said interaction space ,inenergy exchanging relationship with wave energy traveling along said structure, the average motion of said electrons being along the length of said structure, said electron beam being injected into said interaction space along a region nearer said structure than said electrode, said structure being negative with respect to said electrode, said structure being at least partially surrounded by said electrode, said structure being maintained negative with respect to said electrode.

11. A beam reentrant traveling wave electron discharge device comprising a periodic slow wave energy propa gating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetwcen, an electron source, and means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with Wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of wave ener y along said structure, said structure being maintained at a potential negative with respect to said electrode, said electron beam being injected Within said interaction space along a region nearer said structure than said electrode.

12. A beam reentrant traveling wave electron ,discharge device comprising a periodic slow Wave energy propagating structure for transmitting electromagnetic wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of Wave energy along said structure, said structure being maintained at a potential negative with respect to said electrode, and output energy coupling means disposed adjacent one end of said structure.

13. A beam reentrant traveling wave electron discharge device comprising a periodic slow Wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in tr e region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of wave energy along said structure, said structure being maintained at a potential negative with respect to said electrode, output energy coupling means disposed adjacent one end of said structure, and signal input coupling means located adjacent the other end of said structure.

14. A beam reentrant traveling Wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining .a continuous interaction space therebetween, said electrode being capable of electron emission, and means for directing a beam of electrons along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of Wave energy along said structure, said structure being at least partially surrounded by said electrode, said structure being maintained at a potential negative with respect to said electrode.

'15. A beam reentrant traveling Wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, said electrode forming at least a portion of an evacuated envelope, means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of Wave energy along said structure, said structure being maintained at a potential negative with respect to said electrode, and cooling means including a fluid containing conduit positioned within and arranged in thermally conductive relationship with the envelope portion of said electrode.

16. A beam reentrant traveling Wave electron discharge device comprising a periodic slow wave energy propagating structure for transmitting electromagnetic Wave energy, an electrode spaced from and substantially coextensive with said structure, said structure and said electrode at least partially defining a continuous interaction space therebetween, an electron source, said electrode forming at least a portion of an evacuated en velope, means for directing a beam of electrons emanating from said source along said interaction space in energy exchanging relationship with wave energy traveling along said structure, said means for directing including a magnet and a potential source coupled to said structure and said electrode for producing mutually transverse electric and magnetic fields in the region of said interaction space substantially perpendicular to the beam of electrons in said interaction space, said magnetic field being disposed substantially transverse to the direction of transmission of wave energy along said structure, said structure being maintained at a potential negative with respect to said electrode, and cooling means including a fluid containing conduit arranged in thermally conductive relationship with the outer surface of the envelope portion of said electrode.

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